This invention relates to a polymerization process and in particular to a method of polymerizing ethylenically unsaturated monomers by classical free radical polymerization. These monomers include unsaturated carbon-carbon bonds which are broken during polymerization, such as alkenes, various vinyl halides, acrylics, and acrylonitriles. The invention has applicability to a wide range of direct homo- and copolymerization processes, including bulk, emulsion, suspension, solution, and precipitation processes.
Classical free radical initiated polymerization of ethylenically unsaturated monomers is carried out by means of a small quantity of an added initiator which, under the reaction conditions, breaks down to form a free radical. The free radical activates the carbon-carbon double bond of the monomer and initiates chain growth. Under varying reaction conditions, the same compound can act as either an initiator or a chain transfer agent.
Traditionally, the free radical initiator is activated by heat. This approach has a number of drawbacks, the most serious of which is the instability of many systems at higher temperatures. Ultraviolet radiation has been utilized to activate free radical initiators, but this technique is of limited usefulness in the presence of pigments, as is the case when monomers in paint are polymerized.